Generally, arrays of electronic devices such as semiconductor dice are held securely in position on adhesive surfaces such as adhesive tapes when they are being singulated from a sheet of wafer. After singulation, the adhesive tape holding the dice can be moved on an XY plane by a wafer table to position each die for detachment from the adhesive tape.
To detach a die from the adhesive tape, vacuum force is applied on a non-adhesive side of the tape. The die is partially detached from the adhesive tape as a result of the said vacuum force on the tape. Thus, the area of contact between the tape and the die is reduced. Additionally, an ejector pin below the adhesive tape pushes the die upwards from the non-adhesive side of the tape to lift and further detach the die from the tape. The die can usually be removed completely thereafter by a pick-and-place tool such as a collet mounted to a bond arm of a die bonder when the collet applies a vacuum suction force to hold onto on the detached die and lifts it away from the adhesive tape.
Conventionally, pick-and-place die bonders comprise single bond arms for picking up semiconductor dice. As the size of a die decreases and the number of dice per wafer increases, two or more bond arms can be used to increase throughput, which is calculated in units per hour (UPH). For instance, Japanese publication number 63-100737 entitled “Die Bonding Process” discloses a bonding apparatus including four rotary bonding arms. Each bonding arm has a bonding tool at one end which is at a fixed radial distance from the center of rotation and at equidistance from one another. Therefore, one bonding arm may pick up a die at one location when another bonding arm is bonding a die at another location, resulting in a decrease in bonding cycle time.
However, this approach may bring about problems relating to the difficulty of maintaining a common pick-up point during die detachment. For example, the alignment of the collet on each bond arm to the wafer and the ejector pin is dependent on a distance between the center of rotation of the bond arm and the collet, and requires close monitoring and adjustment. Thermal expansion of the bond arms during the pick-and-place process is one factor that would affect the alignment between the collet and the ejector pin. Therefore, it would be desirable to devise an actuator for automatically aligning the ejector pin with the collet at all times at the pick-up point.